The present invention relates generally to an improved apparatus and method for filtering fluids that is particularly useful for filtering lubrication oil or other fluids for internal combustion engines.
One of the more common methods of cleaning fluids is filtration. Such filtration involves separating insoluble particulate matter from the fluid by passing the fluid through a filter medium which traps and retains the particulates. Fluid filters essentially act as a strainer to remove contaminants from both liquids and gases. Contaminants include particulates and deposits that can naturally form in some fluids and negatively affect system operation, life or reliability. Therefore, effectively cleaning such fluids is desirable.
Fluid filters typically incorporate a disposable circular cylindrical filter element (or cartridge) which has a perforate central supporting core contained within a casing. The filter element is usually assembled by wrapping multiple layers of filter media around the central supporting core. The filter element is then traditionally mounted within the casing having an inlet for the unfiltered fluids, or influents. Typically, the influent enters the casing under pressure and then flows radially through the multiple layers of filter media. The filter media catches and retains contaminants as the fluid passes through the filter element. After the fluid completes flowing through the radial filtration path, the filtered fluid is drawn off from one end of the supporting core and reused. Similar filters for fuel, gas, air and other fluids are well known.
Such known filtering apparatus have incorporated filter elements consisting of concentric layers of filter media. Typically, an outer layer of filter media is formed of a relatively coarse filter media such as a wood excelsior. Coarse filter media has larger pore sizes and is designed to trap and retain larger contaminants. An inner layer is usually formed of a relatively fine filter media such as a cotton fiber batt. The fine filter media of the inner layer has smaller pore sizes and filters out the smaller contaminants as the fluid travels toward the central supporting core. Examples of such filter elements are described in U.S. Pat. No. 3,384,241 and 4,187,136 issued to William G. Nostrand.
The filter elements described in the United States Patents cited above tend to plug prematurely due to a buildup of contaminants towards the outer surfaces of either the coarse layer or the fine layer of filter media. The inner filter media often does not get used because the fluid cannot reach those layers. As a result of this buildup, much of the filtering capacity represented by the full thickness of the filter media cannot be utilized before the used filter element must be disposed of and replaced with a new filter element.
A filter element which operates more efficiently than prior filter elements comprising concentric filtering layers is shown and described in U.S. Pat No. 4,938,869, which is owned by the assignee of the present invention. This improved filter element comprises relatively long lengths of different filter media wound about the supporting core to form spiral convolute layers. This filter element prevents premature plugging by directing the influent through the filter element along both radial and circumferential flow paths that expose all portions of the filter media to the fluid. Like previous filters, the filter media can include wood excelsior and a batt of cotton material, although other filter media can also work well. If one area of the filter element becomes plugged, the filter element simply directs the fluid flow along an alternative path where clean, effective filter media is available. This improved filter element eliminates premature plugging and the need to replace the filter element until all the filter media of the filter element is plugged with contaminates from the filtered fluid.
The single disadvantage associated with the filter element configured spirally as described above is that, if the filter element is not replaced at the time the filter media comprising the filter element reaches capacity or is plugged, the unfiltered fluid is directed circumferentially between the layers until the fluid reaches the perforate central supporting core. On reaching the perforate central supporting core, the unfiltered fluid exits the filter assembly and is collected as effluent. In such cases, in addition to not being properly filtered, the unfiltered fluid is often combined with and contaminates filtered fluid.